Impact perforation of polymer-metal laminates: projectile nose shape sensitivity

Recent research has established that polymer–metal laminates are able to provide enhanced impact perforation resistance compared to monolithic metallic plates of the same mass. A number of mechanisms have been proposed to explain this benefit, including the dissipation of energy within the polymer itself, and the polymer deformation enhancing dissipation within the metallic layer. This understanding of the layer interactions and synergies informs the optimisation of the laminate. However, the effect of the nose shape geometry of the projectile on perforation resistance of a particular laminate configuration has not been established. An optimal laminate configuration for one projectile may be sub-optimal for another. This investigation aims to clarify this nose shape sensitivity for both the quasi-static and impact perforation resistance of light-weight polymer–metal laminates. Bi-layer plates are investigated, with a polyethylene layer positioned on either the impacted or distal face of a thin aluminium alloy substrate. Three contrasting nose shapes are considered: blunt, hemi-spherical and conical. These have been shown to induce distinctly different deformation and fracture modes when impacting monolithic metallic targets. For all projectile nose shapes, placing a polyethylene layer on the impacted (rather than distal) face of the bi-layer plate results in an increase in perforation resistance compared to the bare substrate, by promoting plastic deformation in the metal backing. However, the effectiveness of the polymer in enhancing perforation resistance is sensitive to both the thickness of the polymer layer and the nose shape of the projectile. For a thin polyethylene layer placed on the impacted face, the perforation resistance is greatest for the blunt projectile, followed by the hemi-spherical and conical nose geometries. As the thickness of the polymer facing layer approaches the projectile radius, there is a convergence in both failure mode and perforation energy for all three nose shapes. Bi-layer targets can outperform monolithic metallic targets on an equal mass basis, though this is sensitive to the type of polyethylene used, the polymer layer thickness and the projectile nose shape. The greatest benefit of bi-layer construction (on an equal mass basis) is seen for blunt projectiles, using a polyethylene that maintains a high degree of strain hardening at high strain rates (i.e. UHMWPE), and a polymer thickness just sufficient to switch the failure mode in the metal layer from discing (failure at the projectile perimeter) to tensile failure at the plate centre

Impact performance of composite sandwich structure under high velocity impact

Composite sandwich panels are well known for their relatively high stiffness over weight ratio and have been increasing utilized in various applications where the weight of the structure is a key design concern, e.g. in aircraft and aerospace components. However, these structures are vulnerable when subjected to a transverse impact loading. In this paper, the impact performance of composite sandwich structures with foam core is investigated. In particular, the idea of multi-layering the core by foam layers of different density and its effect on the energy absorption under low and high velocity impact is of interest. In this study, composite sandwich panels made of Glass Fibre Reinforced Polymers (GFRP) for skins and PVC foam for the core are used. Two different arrangements of foam core are considered: uniform core (80/80/80 kg/m3 ) and graded core (100/60/100 kg/m3 ). Both of these core arrangements have the same areal density. Low (up to 5 ms-1 ) and high (up to 200ms-1 ) velocity impact tests were performed using a drop tower and a gas gun respectively. In-plane and out-plane properties of composite sandwich samples were measured employing 2-D and 3-D Digital Imaging Correlation (DIC) methods. The results indicate that the composite sandwich structure with graded foam core has a better energy absorption capability compare to the one with uniform foam core

Spray deposition of graphene nano-platelets for modifying interleaves in carbon fibre reinforced polymer laminates

This study describes a novel and versatile method of incorporating graphene nano-platelets (GNP) into compos-ite laminates to investigate its effect on mode I and mode II interlaminar fracture toughness (ILFT). Non-woventhermoplastic veil interleaves have been modified by spray deposition with a GNP dispersion to give either a con-tinuous or strip-patterned distribution. The coated interleaves were used to modify the interlaminar region ofcarbonfibre reinforced polymer (CFRP) laminates. The fracture surfaces were characterised by scanning electronand optical microscopy.The continuous GNP distribution in mode I prevented the formation of carbonfibre bridging, resulting in similarinitiation and propagation values. In mode II, the increased thickness of the interlaminar region, coupled with theuneven fracture surface showed the highest increase in the mode II ILFT for the continuous GNP distribution. Thestrip-patterned GNP distribution showed reduced carbonfibre bridging compared to the baseline CFRP and ther-moplastic interleave laminates. This may be due to small scalefibre bridging between the deposited GNP-stripswhich also lead to peaks and troughs in the load-displacement response. In mode II, it is suggested that the de-posited GNP-strips were sufficiently tough to re-direct the propagating crack from the modified interlaminar re-gion to the adjacent ply

The high velocity impact resistance of fibre metal laminates

The high velocity impact resistance of fibre metal laminates (FMLs) based on combinations of three different aluminium alloys (6161-O, 6061-T6, 7075-T6) and a glass fibre reinforced epoxy resin have been investigated both experimentally and numerically. A series of perforation tests on multilayer configurations, ranging from a simple 2/1 lay-up to a seven ply 4/3 laminate. High velocity impact was conducted using a projectile gas-gun launcher, operating in the velocity range between 119 m/s and 252 m/s.[1] The impact response of fibre metal laminates samples was characterised by determining the energy required to perforate the panels. A stereoscopic Digital Image Correlation (DIC) method was adopted to measure full-field deformations and strain for FMLs which providing the full field strain history and 3D measurements up to sample perforation. The perforation resistance of the panels was predicted using the finite element analysis package Abaqus/Explicit. A vectorized user-defined material subroutine (VUMAT) was employed to define Hashin’s 3D rate-dependant damage criteria for the composite layers. The subroutine was implemented into the commercial finite element software ABAQUS/Explicit to simulate the deformation and failure of FMLs. Agreement between the predictions of the finite element models and the experimental data was good across the range of configurations. Ballistic limit of those FMLs was obtained from both the experimental tests and numerical approaches

Soft impact response of laminated glass plates

A laminated glass typically consists of two layers of glass and one layer of polymer. It is utilised in many applications in which the glazing is exposed to external threats like impact or blast. In this paper, damage development of laminated glass plates by soft impact is investigated in both low and high velocity regimes. Low velocity impacts (up to 4 ms-1 ) were conducted using a drop tower. Soft impact was achieved by attaching a silicon rubber cylinder to a flat steel impactor, with a diameter larger than that of the rubber, which itself is backed by a 16.9 kg weight. Different velocities were obtained by dropping the weight from various heights. For high velocity impacts (up to 220 ms-1 ), a gas gun apparatus was used. The silicon rubber cylinder was fired, using a sabot, in a 25 mm diameter barrel. High speed photography was employed to monitor the deformation and damage development in the laminated glass samples. Laminated glasses with different types of polymer interlayer were tested. The results show a better impact resistance for laminated glass with a stiffer polymer interlayer at both low and high velocity regimes

The high velocity impact resistance of fibre metal laminates

The high velocity impact resistance of fibre metal laminates (FMLs) based on combinations of three different aluminium alloys (6161-O, 6061-T6, 7075-T6) and a glass fibre reinforced epoxy resin have been investigated both experimentally and numerically. A series of perforation tests on multilayer configurations, ranging from a simple 2/1 lay-up to a seven ply 4/3 laminate. High velocity impact was conducted using a projectile gas-gun launcher, operating in the velocity range between 119 m/s and 252 m/s.[1] The impact response of fibre metal laminates samples was characterised by determining the energy required to perforate the panels. A stereoscopic Digital Image Correlation (DIC) method was adopted to measure full-field deformations and strain for FMLs which providing the full field strain history and 3D measurements up to sample perforation. The perforation resistance of the panels was predicted using the finite element analysis package Abaqus/Explicit. A vectorized user-defined material subroutine (VUMAT) was employed to define Hashin’s 3D rate-dependant damage criteria for the composite layers. The subroutine was implemented into the commercial finite element software ABAQUS/Explicit to simulate the deformation and failure of FMLs. Agreement between the predictions of the finite element models and the experimental data was good across the range of configurations. Ballistic limit of those FMLs was obtained from both the experimental tests and numerical approaches